A pilot or observer in an aircraft, shuttle vehicle or other airborne vehicle normally flies by visual observation, radio control, radar control or computer control. Avoidance and identification of other objects at a finite distance in airspace or space is also done visually or by illumination of the object by radar, by a laser, by a high-intensity light or by sound waves and subsequent sensing and observation by the human eye of a returned and processed visual signal. This signal may be one from direct observation of the object by the eyes or from a display to the eyes from a television camera, infrared detector, radar or sonar screen or by a remote, shared communication link. The human eyes have a good degree of stereo depth perception ideally covering objects at distances of less than 10 meters. Less ideally, objects at up to about 100 meters distance can also be seen to have some depth but the ability to "see" depth in an object increasingly fades beyond the 100 meter distance.
This phenomenon is particularly acute when the airborne vehicle is flying at high speeds when the finite time to pick-up and observe an object is very small. The time left to avoid an object or lock-in on the object, in the case of a military aircraft desirous of firing at the object, is also increasingly small as closing speeds increase.
When the objects are perceived without depth perception, it becomes harder to pick up the object against its background, be it space, clouds, mountains, or other terrain and to visually determine its approximate distance from the observer. Additionally, no shadows can be seen on the object. Thus, while shadow, haze and the convergent lines of perspective at infinity give some clues as to distances when objects are over 100 meters distance from the human observer, human imaging skills lessen greatly and the ability of the pilot to properly guide the craft is lessened. The primary reason for loss of depth perception is the relatively small baseline between the human eyes, which does not permit a human to have much depth perception of objects at a distance greater than about 100 meters.
Aircraft warning systems have been proposed such as seen in U.S. Pat. No. 3,053,932 in which cameras mounted above and below an aircraft fuselage continuously scan in hemispherical areas about and below the aircraft with radar, infrared or ultraviolet radiation to detect an object and present separate pictures in the form of a visual display of surrounding air space to the pilot. If a clearer view is desired, the pilot can switch to a telephoto lens or a camera can be locked on to the object.
As seen in U.S. Pat. No. 3,518,929, multiple cameras have been employed to simultaneously photograph a scene where all the cameras have a common film transport mechanism and have optical axes convergent on the scene. According to that patent the convergent axes may be altered to permit convergence at a distance other than 26 feet.
U.S. Pat. No. 3,608,458 illustrates a fish eye type camera for taking wide angle stereoscopic pictures where the lenses have a predetermined operative angle with respect to each other. U.S. Pat. No. 3,697,675 shows a stereoscopic television system in which a pair of monochrome TV cameras view the same scene from two separated and variable positions and, with appropriate circuitry, supply color signal separate images of different color which are produced on a color TV receiver. When viewed through special glasses, a three dimensional scene is perceived.
Airborne stereoscopic scanners of terrain below an aircraft are seen in U.S. Pat. No. 2,949,005 in which an image from a first position of the scanner is displayed and then one from a second position of the scanner to give a stereo effect. Scanning is in the direction of the flight axis. U.S. Pat. No. 3,670,097 discloses prior art stereoscopic television systems in which two separate cameras and two separate receivers transmit right and left optical images. U.S. Pat. No. 3,784,738 shows (FIG. 11) use of spaced separate image tube cameras and headgear for receiving signals. The distance between the cameras is the average eye interpupillary distance of a human.
The text entitled The World of 3-D by Jac. G. Ferwerda published by Netherlands Society for Stereo Photography, 1982, also describes stereo photography using two cameras.